1. Field of the Invention
The present invention relates to methods of communicating between a high side device driver and a low side controller without using a level shift circuit.
2. Brief Description of the Prior Art
Most circuits in power processing applications use a xe2x80x9chigh side devicexe2x80x9d that needs to be controlled (i.e., turned on or off at predetermined times) to process the power. These devices (IGBTs, FETs, bipolars and other devices) utilize a xe2x80x9cdriver ICxe2x80x9d that raises its gate above its source to turn it on. As during the turn on process, the source/emitter also rises substantially above the -ve rail of the DC bus (to which the main controller is typically referenced). This causes the driver to xe2x80x9cfloat upxe2x80x9d with the device source voltage. Consequently, high voltage ICs (HVICs) with internal level shifting switches typically are used to communicate the xe2x80x9con/offxe2x80x9d signals to the driver of the gate. A typical prior art circuit is illustrated in FIG. 1.
Referring to FIG. 1, a controller 2 communicates with a power switching circuit 4 by way of HVIC 6. The switching circuit includes high side switch 8 and low side switch 10. A high side driver 12 and a low side driver 14 of the HVIC 6 are associated with the high and low side switches 8, 10, respectively. The two switches are connected in series between a high voltage rail and ground. The high voltage rail typically carries hundreds of volts. In contrast the controller 2 typically operates in the 5 volt range. Consequently, in order for the controller 2 to communicate with high side switch 8, a level shift circuit 16 is incorporated in HVIC 6 to communicate the low voltage signal from controller 2 to the high side driver 12. The circuits operate to generate a signal at output 18. Typically, the controller alternates opening and closing the two switches to generate a high voltage square wave, for example.
In some cases, the high side driver also performs xe2x80x9cfault protection.xe2x80x9d This involves sensing a parameter in the high side switching device, such as current or voltage, for example, and turning off the device to protect it from failure in the event that the parameter exceeds a certain value. The decision is then communicated to the controller by means of a level shift down device. An example of such a prior art circuit is shown in FIG. 2.
Referring to FIG. 2, a controller 20 communicates with a power switching circuit 22 by way of HVIC 24. The switching circuit includes high side switch 26 and low side switch 28. A high side driver 30 and a low side driver 32 of the HVIC 24 are associated with the high and low side switches 30, 32, respectively. The controller 20 communicates with high side switch 26 by way of a level shift up circuit 34, similar to the circuit shown in FIG. 1. Fault protection information generated by protection circuitry in driver 30 is communicated back to controller 20 by way of a level shift down circuit 36.
Accordingly, the need exists for a technique for communicating between a high side driver circuit and a low voltage controller without requiring level shifting circuitry.
The present invention provides analog and digital methods of achieving communication with the high side driver without requiring an HVIC with an internal level shift circuit.
A preferred circuit according to the present invention includes a low voltage controller with time coding circuitry generating an output, such as a voltage, a current, or a digital signal. A driver includes circuitry for decoding the output and controlling a high voltage switch. Circuitry for communicating between the controller and the driver is provided which does not require level shift circuitry. The driver decodes the signals received from the controller to generate on and off time pulses for controlling the switch.